I don’t think you have to worry about this year. Your FAFSA was correct on the day you filed. If your custodial parent had a new job (not reflected in the prior prior tax year) or had won the lottery AFTER you filed, you wouldn’t have to report that until the next time you filed.
So sorry about your loss. If you lived with your mother for more than half of 2020 (July 2 is the cut off date), her estate may be able to claim you as a dependent for 2020. You may be able to use her as your custodial parent for filing the FAFSA in 2020 too (you lived with her more in the 365 days before the Oct 1 FAFSA filing). You should check with your FA office or with a tax expert.